


My Dark Soulmate

by 2LeryBarBles7



Category: Undertale (Video Game)
Genre: :), Alternate Universe - Dreamtale (Undertale), Alternate Universe - Lusttale (Undertale), Fluff and Smut, I made more of this, Let Nightmare be soft and scary!, Lust deserves better, Lust learning to interact with the gang, M/M, Nightmare is not exactly good, Porn with Feelings, Soulmates, They are all good, but he is not that bad, he cares, so i did this, they are in love
Language: English
Status: In-Progress
Published: 2021-01-28
Updated: 2021-03-03
Packaged: 2021-03-13 16:07:24
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 4,017
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29031405
Author URL: https://archiveofourown.org/users/2LeryBarBles7/pseuds/2LeryBarBles7
Summary: Everyone in the multiverse had a soulmate, is just a recent thing that occurred and now even the Guardians could hear the calling of their destined, sometimes a soft and warm voice that guided them, others were melodic like a song or heated with passion.What Nightmare heard was an agonizing plea for help and a cry that would have haunt him forever if he hadn’t found his soulmate the moment he did.
Relationships: Nightmare/Lust, Sans/Sans (Undertale)
Comments: 17
Kudos: 121





	1. Encounter with my soulmate

**Author's Note:**

> Happy Birthday to Lust!!

**“You poor thing”** murmured the dark guardian looking to the tormented soul that had been calling for him. His own soul was twisting painfully at signt of the torture that his destined was subyected to before he could prevent it.

Nightmare carried the unconscious skeleton carefully, fearing that one wrong move would damage him even more. A pathetic groan made him look down to the rest of the monsters around, many of them already dusting from the wounds that the darker made. His eye-light glowed dangerously while his tentacles finished those scum for monsters.

**“Death is just too good for the likes of you but consider yourselves lucky that he needs my attention even more than you lot”** he hissed crossing a portal back to his castle. He had a mate to take care of.

\-----------------------------------

Purpley eyelights glowed softly in confusion, the young skeleton couldn’t understand where he was and how he got there. Inspecting his situation better he noticed that his tattered clothes were replaced with a soft nightgown and all of his wounds were almost gone. 

“You are awake” said a soft and calm voice from the door that just now noticed. Another skeleton was there, Cross was his name if remembered well from the stories that Ink had told them. That could only mean that he was in Nightmare’s castle, sudden panic made his soul shake and quiver. Why was he inside the liar of the Bad Sanses? Tears started to fall from his eye sockets while Cross tried to console him with a worried expression. 

**“Cross you are dismissed”** ordained Nightmare himself while looking at both skeletons, the monochromatic monster nodded and marched down the corridor giving them privacy. 

The King looked at his soulmate with sadness, he was feeding from his doubts and fears and all of the  _ what if’s _ that others had pounded into his mind about the terrors of being in the Dark Domain. Nightmare got closer to the crying skeleton and caressed the tears off his face.

**“Lust, my little soul, you are safe here”** cooed the darker, his tentacles twitching impatiently for being so close and, somehow, still so far from his soulmate. 

Lust stopped his crying after a few moments, tender arms held him softly and the calling of his soulmate was luling his worries away, he felt calm. He opened his eyes just to catch a single teal eye-light looking at him with worry and adoration. 

**“Feeling better my soul?”** asked Nightmare with a soft voice the Lust had only heard in his dreams. 

That made his mind click, not so long ago the Star Sanses informed everyone in the Council that there were starting to appear soulmates around the AU’s, someone who would complement them, someone who would love them and protect them. He was safe, he was in the arms of his soulmate. Nightmare asked again since Lust was not answering, he nodded, not trusting his voice to not crack or to say something inappropriate, he felt Nightmare’s tentacles caressing his tired bones carefully like he was something valuable and not a miserable whore.

**“You should stop those negative thoughts, I can sense them”** taunted Nightmare, making him look up again, when did he lower his head?

“Sorry” he murmured unsure.

Nightmare sighed softly and took one of Lust’s hands on his inspecting the little cracks that were almost completely heal, his tentacles feeling the rest of the injuries. He felt angry again, he should had called his crew to take the offenders to the dungeons for torture instead of a quick death.

**“Can you tell me what happened to you?”** Nightmare’s tone was more of a growl than a question, Lust felt glad that the intent wasn’t directed to himself.

“Just some monsters that didn’t like when I said no, I was just returning home from my job when those guys intercepted me, you know my job, everyone does, they were some of the clients that always want something for free but I refused this time, they got mad, their LT was too high and I was too tired, I tried to fight them off but…” Lust couldn’t continue but Nightmare only needed that, he cursed his soulmate’s world under his breath. 

Nightmare hold him closer, cleaning his tears away  **“Do you like your universe?”**

Purple eye-lights shined in confusion, he didn’t expect that question.

“Not really, why?” he answered looking back to the darker.

**“I want you to live here with me and my crew, I don’t like the implication of you constantly being harassed but I don’t think that you would like for me to kill anyone that tries anything on you”** offered Nightmare, kissing the palm of Lust’s hand.

Lust blushed deeply, his mate wanted him to live with him, even though he knew about the profession that made many others turn their backs to him. He thought about it, about not having to sell his body for food or protection, to live with his soulmate and the ones that were under his orders, all of them so loyal and fierce. To not have to live with touches that he didn’t want. 

“My brother” he murmured preoccupied. Would Pink and Metta stay in that hellhole? 

**“He and his mate can live here too if you want or I could accommodate them in one of the AU’s under my reign”** said Nightmare reassuring him. He wanted to please his mate.

“You sure?” 

**“I did the same for Horror, he asked for his brother and the fire elemental to stay in the castle since it was the best place for them at the moment, they still live here, none of them have to do any of the work that the crew does. Most likely they will work in the castle or even in the little kingdom that is starting to grew”** Nightmare explained. He was starting to need more help since some survivors of neutral time-lines around the multiverse decided that they were better under his protection.

That made Lust feel better, a part of him was fearing that his brother would have to kill or something to stay in the castle. But there was still a question in his mind. 

“And what would I do?” he asked curiously.

**“You would be my Queen”** said Nightmare, kissing him softly. 

There was no way that Lust was going to say  _ no _ to that.


	2. My Beloved Soulmate

**Summary for the Chapter:**

> Part Two of My Dark Soulmate   
> Patience is a virtue, but they are both sinners so fuck it.

It’s been a few weeks since Lust found out that his soulmate was Nightmare, a lot of things changed for everyone in the castle and the little AU; the announcement of the new Queen was quite a celebration, the crew was ecstatic for their boss and so were the monsters under his protection. 

Lust found himself surprised with how easily the group of maniacs had accepted him into their home. And how nice their company was once he let go of all of his prejudices, he cursed the Star Sanses and the rest of the Council more than once since the first day of his stay in Nightmare’s castle. He was doing the same thing that many others did to him, he decided to be better than that, so he started to pass the time with the crew.

He found out that Horror loved to cook, they hung out in the kitchen a lot since Lust was a picky eater, and because he liked to see him work, he was the easiest to deal with too, just giving him some food could calm him if he was having an episode or if he was too hungry to think. 

Dust was difficult at first, something to do with the hallucination of his death brother, but soon Lust found something to do with him, dancing was a great exercise, besides fighting and sex, and that helped with the excess of LV and energy, it also made him concentrate more in the moves than in the malicious words that the Fake-Pap could say. 

Killer was a tease but that was ok with Lust since he was a master of teasing back, the first time he did it he almost cracked a loud laugh when Killer just stopped and acted like he didn’t know what to do next, more than once the rest of the group could find them just talking in a very dark or crude humor. 

Cross was like a lost puppy in Lust’s opinion, he was the newbie, still trying to find his place in a world too dark and inmoral compared to the way he was raised, he was soft spoken when he was not in the middle of a battle and he was the one to help him understand how royalty work when Nightmare was occupied, he found himself appreciating the company of Cross when the other three were too chaotic or dangerous to be around. 

But his favorite was his soulmate, Nightmare was very quiet and didn’t act sweetly at first like many partners that he had seen but he had his own way to show affection to Lust; they could chat for hours to an end about nothing, everything, Nightmare was a huge nerd under all that goop and loved to tell him as much as Lust wanted, never losing his patience if he didn’t understood some things. Also his tentacles were always over him, caressing his hips, his arms, his neck, basically everywhere without making it feel sexual, just nice and tender.

But Lust wanted more than that, don’t take him wrong, the actual affection was amazing, he had never felt as happy or as loved before, but his body was starting to crave something more intimate, his LT was starting to act up and he  _ needed _ his King to take him and mark him as his.

\------------------------------------

Nightmare was on edge to be honest, just the idea of having a soulmate was confusing for him; his whole life he had been feared, rejected and hated, to suddenly gain someone that could accept him, like his gang did, and even love him. It was too much.

He desired those feelings, he wanted the affection that he could only ask a lover for. But he was also scared of them, he was scared that he would drive away his soulmate if he did the wrong move. But he wished for more every time Lust acted excited around him, how he looked at the darker like he was more worthy that he felt deserving for. He needed more of that, he wanted to make Lust  _ his. _

But Nightmare also wanted to wait until he could stop feeding from the dark emotions that Lust felt against himself, all the hatred that others pounded into his mate, all the objectification that he suffered. He kept his actions in check so there was just protection and love in his intent instead of the heated passion that he also wanted.

He was willing to wait for his partner to be ready, enjoying every moment of Lust’s excitement for discovering something new or just for being accepted in their little family of ragtags. He wanted to wait until the coronation of the new Queen to mark him.

At least that was his idea up to the moment he saw  _ his _ mate in  _ their _ bed looking like he was sin incarnated. 

Lust looked gorgeous, his face glowing softly in a delicate violet, eye-lights looking at Nightmare adoringly, a beautiful ecto framed in a delicate see-thru garment made of silk. 

**“My little soul, what is the meaning of this?”** asked Nightmare in a deep purr of delight. 

“I just wanted to give you a surprise” Lust smiled, he was so glad for the reaction he was getting from his soulmate.

Nightmare stepped closer, his tentacles stretched impatiently towards Lust, one of them caressing his face lovingly while the others started to explore his ecto. Soft curves, warm magic, the  _ oh so sweet aroma of his mate’s heat _ . He wanted to ravish him, to take complete control over him and mark every single inch in that beautiful body. But he stopped, he needed to know first.

**“And you are ready, my soul?”** asked Nightmare, sitting at his side and making the bed sink under his weight.

Lust smiled and caressed his King’s face closer to him, he kissed him softly, placing all of his intent into love and adoration, he wanted this, the wanted  _ Nightmare. _ And Nightmare wanted him too for the way he returned the kiss; a cyan tongue entering in his mouth as he gasped at the feeling of the darker intent;  _ Love, love, love, need, want.  _ Stars, Lust trembled under Nightmare’s aura.

**“I’m going to make you mine”** he declared, his tentacles retracting back into hiding. Not being needed at the moment. 

**“I'm going to take my time mapping out your body.”** his hands started to explore, searching for every single place that would recompense him with a moan or a beautiful expression. 

Lust gasped softly, Nightmare’s hands were so light, giving him only phantom sensations that made him crazy, he felt them everywhere, in the nuk of his neck, down to his sternon and barely over his breasts, finally pressing and pinching his nipples, teasing him. The single eye light observing every reaction, feeding from the raw emotions, that intoxicating frustration, the  _ need _ . It was so beautiful. 

He wandered lower, his phalanges finally touching the wet and heated entrance; he rub Lust’s clit softly, running his fingers along the slit making little no not pressure, just enough to make his soon-to-be Queen moan and purr. Every sound going directly into his magic. Nightmare dipped in just a little, Lust whined, tears starting to form in his eye-sockets. 

“P-please, Night” Lust moaned, he wanted more, he wanted his King  _ inside _ , deep into his magic. 

Nightmare kissed him deeply, playing with their tongues while lowering his shorts just enough to release his cock. Tentacles getting out too, moving Lust into a better position, their ectos rubbing against each other making both moan and groan. 

The darker pressed into Lust’s heat, entering with little resistance, the violet skeleton cried in pleasure, his magic accommodating his lover, his soul singing pleas of  _ more, more, more.  _ Nightmare groaned once he bottomed out, taking a minute to watch his partner’s face, he loved it, the warm and tight feeling around him, his soul trembling with how  _ right  _ it felt to be inside his soulmate. 

He started to move, pulling back slowly, dragging the feeling of how deep he was, to then push back inside in a quick thrust that made Lust moan, the rhythm changing every time, to Lust’s enjoyment and Nightmare satisfaction. The darker slamming into his lover’s cunt while a tentacle played with his clit and the others cupping his breasts, twisting his nipples. The room is heavy in the aura of their magics, the heat and sheer intent. 

They feel closer to their release, souls beating and calling each other.

**“I will mark you, I will mark your very soul and everyone will sense it, they will sense me in you, my power around you always present”** murmured Nightmare against his neck, kissing and nibbling, preparing the place he was going to mark. 

“Yes, yes please, Nightmare, I’m yours my soul, my King” babbled Lust, his eye lights hazy but he was conscious enough to see their souls invoked and out of their chests; his violet and dripping, Nightmare’s dark but beautiful and heavy with magic. 

Their souls touched, making them moan and tremble, the protective shells around them vanishing, making the contact so much tipping them into the limit, Nightmare cumming deep inside his womb as he _bit_ right into ecto and bone making marrow pour in his mouth. Lust crying in pleasure as he cums and pleads and purrs. Their souls imprinting the others magic, marking them as one.

Nightmare lapped over the mark and arranged them into a better position, Lust cuddling in his arms, full and warm and so  _ loved. _ His tentacles around the pair keeping them close and protected. 

**“I love you”** murmured Nightmare looking at his Queen fall asleep. Soon he would present him to everyone, he just needed a little more time.


	3. Planning for the future

**Summary for the Chapter:**

> After their little, and private, celebration the King and Queen still had more things to do, like finish the preparations for the Coronation and maybe take care of the problem that is the Multiversal Council… Actually… Maybe they should do something about the Council first.

“This is wrong and is starting to get out of hand! They can’t keep doing this to us” yelled Lust in frustration. Tears accumulated in his eyes sockets but none were shed yet.

Nightmare nod in agreement, he was extremely tired and hurt, lately the rest of the Multiverse had decided to combine forces and try to actually kill them on sight, it didn’t matter if it was only one of them or the whole group or if they had been doing anything at all. Their heads had a weight in G’s in the eyes of their enemies.

 **“It might be wrong but nothing in our lives has ever been fair”** Nightmare’s voice was gloom, almost defeated.

“There must be something that could be done, I don’t know what I would do if one day any of you is not back from one of your missions” Lust sighed and looked at everyone in the group.

They had just returned from a simple recon mission that ended up with all of them nearly dusting. It wasn’t just the Council anymore, more monsters were being trained and selected to fight them all, Horror was the worst case this time, someone made a team of Undyne's tag against the broken skeleton sending him into a panic attack that had the entire crew distracted enough for the rest of their enemies to act and made bolder moves. 

They escaped by pure luck.

Their luck was beginning to run down.

“At this rate our world will be left defenseless” said Pink in distress, there were very few monsters with enough LV or combat skills living in the growing village. 

“We need more allies, we have power but our numbers are too low while the enemy has entire armies. It would be difficult to find them but not everyone in the multiverse is against us, we just need to be careful at the moment to select them” said Cross, his mind running with strategies, his military uprising showing.

“You make it sound like we are preparing for war Criss-Cross” the contemplating tone in Killer’s voice made the rest of the gang fall into silence.

“I will take no risk, if it’s a war what they want then is a war what they will get” the soldier said, voice cold and low, devoid of his usually good nature.

“We will need more than that if we go to war, we might need to contact Error too” commented Dust, his magic crackling in his marrow, mismatched eyes locked in the unconscious figure of Horror.

“We could use even the things hidden in the old lab, Alphy’s biggest mistake could help us if we get a way to control it” mused Killer, looking nowhere in particular. 

Lust was terrified with their talk, the implications of a war, of using the reanimated corpses that he had only heard about from other Sanses in the Council, they couldn’t be serious. Pink had the same scared expression but he was also looking hopeless, like there was really no other option for them. 

“I could ask around, other Paps tend to talk without filters, and no one takes me seriously enough some times, so it wouldn’t be difficult for me to get some info about monsters that are not happy with the Stars” said Pink, looking down and uncomfortable.

Lust looked at his brother in disbelief, his mind started to fill with all the many ways this could end wrong, suddenly he couldn’t listen to them all, only an annoying buzzing that covered their planning, his soul feeling like a knot. So many things to say, not one one of them leaving his mouth. The soon to be Queen started to tremble, bones rattling in fury? Fear? Magic boiling inside of him.

 **“Lust?”** Nightmare’s voice called him. 

There were arms around him, grounding Lust back to reality, he felt exhausted, thoughts everywhere and nowhere at the same time, a tentacle caressing his face, taking away the tears that he didn’t know that were falling from his eye sockets. The rest of the gang and his brother were gone, when did that happen?

“Sorry” he said in a weak voice.

 **“There is no need for that”** Nightmare said while carrying him towards their bedroom. 

“But I interrupt in the middle of something serious” Lust hid his face in Nightmare’s sweater.

**“They were saying nonsense”** consoled the King.

“How is planning for war nonsense?!” Lust’s yell was full of anguish and fear.

Nightmare sit down in their bed, his beloved curled up in his lap crying in distress, Lust was more of a gentle soul that he thought, eager to please and to find a way to make everything better for everyone, one would think that they were opposites like him and Dream but the thing with Lust is that he wasn’t blind, he could see and accept and process the negative emotions in a semi-healthy way, especially since he came to the castle. 

The darker waited till Lust calmed down enough for them to continue their talk.

**“We are not declaring war, Cross is right that we need more allies but I will not make anyone fight and risk their lives in a battle that could end up with more loss than gain”** said Nightmare in a firm voice 

**“I have lived for longer lifetimes than anyone, and participating in many wars that ended up in nothing, not even for me, is true that I need the negative emotions to feed myself and my power but wars are tiring and not very worth it, at the end only Reaper wins and the cycle repeats itself once more”** he explained, his single eye light lost in memories of long ago **“the little fights that we had with the Stars were my try into forcing the balance to my favor, it looks like that, even if the negativity is stronger, that doesn’t mean that I won”**

“But then, what are we going to do? Your brother and the Council are after the gang, and we can’t hide here forever” said Lust

**“Why not?”** Murmured Nightmare after contemplating the idea a bit more **“Is not like I need to be present for the negativity to extend, is a natural process after all, I only do those missions to ensure that is not going to end too quickly or that it isn’t too dangerous to the point of growing into a mayor problem”**

“But don’t you need to be there to absorb the energy?” 

**“I could teleport there and hide in the shadows, I don’t need to even be present in the direct conflict just in the same AU, the problem would be that the rest of the gang might grow restless and from time to time some of them have this murderous need”** Nightmare was half forming a plan.

“Maybe we could try and reach for a Fell AU, they are super aggressive and they have LV problems too, they would understand” suggested Lust with a little smile, the idea not being bad, he knew that the Fell faction was always on edge, and only a selected few were even allowed out of their AU, but maybe their could try something different.

**“We have never interacted with a Fell, I feed from their regular negativity but other than that, the pricks are too paranoid and wary, and Red is very elusive”** explained Nightmare.

“I will introduce you directly then, he is a bastard but he is the best one to talk to first, and he owns me a favor, we just need to have a good deal that he can then pass to his brother and then we can meet with the Royal Guards” replied Lust

Suddenly their future was no longer grim and hopeless, suddenly Lust felt like he had control again.

And this time he was not going to let it go.


End file.
